Joint for ceramic materials



' Oct. 3, 1939.

(1:..M. CARINGTON JOINT. FOR CERAMIC MATERIALS Filed March 29, 1959 d/iim,mv

Patented Oct. 3, 1939 PATENT OFFICE JOINT FOR CERAMIC MATERIALS Charles Moiyneux Carington, London, England, assignor to K. L. G. Sparking Plugs Limited,

London, England, a British company Application March 29, 1939, Serial No. 264,778 In Great Britain May 12, 1938 '1 Claims.

This invention relates to joints for ceramic materials such as are used for the insulators of sparking-plugs.

The object of the invention is to provide a gastight joint between a metal part and a ceramic part; this has hitherto presented great difficulty owing to the difiiculty of obtaining a smooth or accurately-dimensioned ceramic surface.

According to one feature of the invention, a

joint between a metal part and a ceramic part comprises two or more intervening layers of soft metal foil. The foil is preferably extremely thin, that is to say, less than 35 of an inch thick. Where the invention is applied to a sparkingplug, the foil must be of metal which will not melt at the working temperature of the plug. Pure aluminium is found to be a suitable material, although other infusible metals could be used.

According to another feature of the invention,

the insulator'of a sparking-plug comprises a metal collar or sleeve fitted to it in a gas-tight manner by the use of a joint as above described. The detachable joint between the insulator and the body of the plug may thus be formed between the metal sleeve or collar and the body.

A specific embodiment ofthe invention will now be described,by way of example, with reference to the accompanying drawing, in which:--

Figure 1 is a sectional elevation of an assem- 80 bled sparking-plug according to the invention,

and

Figure 2 is a diagram explaining the manner in which the gas-tight joint is made between the insulator and the surrounding sleeve.

36 As shown in Figure 1, the sparking-plug comprises a tubular insulator ll! of the ceramic material sold under the registered trade-mark Corundite." The central electrode is assembled in the insulator and forms a firing point II at 1 one end and an electrical contact I! at the other. The insulator is surrounded by a metal sleeve l3 which engages a recess in the body ll of the plug, the insulator being held in place by means of a gland nut l5 or extension tube which engages a metal washer l8 pressing down on to a suitable shoulder l'l formed on the insulator.

The plug is assembled in the following manner. The insulator l0, which is formed with a tapering portion l8, as shown in Figure 2, is closely wrapped with about five layers of aluminium foil of about of a thousandth of an inch in thickness. The foil l9 may be first cut to the required annular shape or, alternatively, the tapering portion' I! of the insulator may be first wrapped and 56 then the wrapped foil cut to the desired length.

A metal sleeve l3 having an internal taper corresponding to that of the portion I8 is then forced on to the foil-covered portion of the insulator under considerable pressure, such as a force of 200 lbs., or, in some circumstances, con- 5 sideraby more. The wall thickness of the sleeve is preferably so small that the sleeve expands resiliently during the forcing operation whereby the foil is tightly gripped between the sleeve and the ceramic insulator. In this manner 10 a perfectly gas-tight joint is obtained between the sleeve and the insulator. The joint between the sleeve and the surrounding body It is easily made gas-tight by accurately machining the co- 1 operating surfaces. The gas-tight joint between the insulator and the foil and between the foil and the sleeve is maintained by the pressure of the nut IS on the shoulder ll of the insulator.

Although the drawing shows an insulator having a tapering portion [8 to which the foil is applied, the invention is also applicable to an insulator having a parallel surface. A collar or sleeve may be drawn on to the foil-covered portion or may be swaged down to form the neces- 25 sary joint.

The invention also consists in providing a gastight joint between the electric contact I2 and the top end of the insulator In. This is achieved by threading a stack of washers 20 of thin aluminium foil, as hereinbefore described, on to the electric contact before this is screw-threaded into the insulator.

It is found that comparatively soft metal such as aluminium, when in the state of very thin foil, 35 penetrates the surface of hard ceramic materials and enables a gas-tight joint to be formed more efllciently than by any known process.

Although aluminium foil has been described, other infusible' metals could be used. The thick- 40 ness of ti of a thousandth of an inch is that which is preferred for the sparking-plug illustrated in the drawing. Somewhat thicker foil, up to $5 of an inch, may be used in some circumstances.

I claim:

1. A joint between a metal part and a ceramic part comprising two or more intervening layers of soft metal foil.

2. A joint between ametal part and a ceramic 50 part comprising two or more intervening layers, each less than 35 of an inch thick, of soft metal foil.

3. A sparking-plug comprising a joint between the insulator and a surrounding metal part which joint comprises two or more intervening layers of soft metal foil.

4. A sparking-plug comprising an insulator, a part surrounding the insulator, and two or more intervening layers, each less than 2 of an inch thick, of soft metal foil.

5. A sparking-plug comprising an insulator, a surrounding metal part, and a plurality of intervening layers of aluminium foil.

6. A sparking-plug comprising a ceramic insulator, a surrounding metal part, and a plurality of intervening layers of soft metal foil 01 about A of a thousandth of an inch in thickness.

7. A sparking-plug comprising a tapering ceramic insulator and a surrounding complementary metal part, wherein the insulator and the metal part are separated by five layers of aluminium foil of about of a thousandth of an inch thick.

I 10 CHARLES MOLYN'EUX CARINGTON. 

